/*
 *                               POK header
 *
 * The following file is a part of the POK project. Any modification should
 * be made according to the POK licence. You CANNOT use this file or a part
 * of a file for your own project.
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2021 POK team
 */

/* @(#)e_log.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#ifdef POK_NEEDS_LIBMATH

#include "math_private.h"

static const double ln2 = 0.6931471805599452862268,
                    two54 = 1.80143985094819840000e+16, /* 43500000 00000000 */
    Lg1 = 6.666666666666735130e-01,                     /* 3FE55555 55555593 */
    Lg2 = 3.999999999940941908e-01,                     /* 3FD99999 9997FA04 */
    Lg3 = 2.857142874366239149e-01,                     /* 3FD24924 94229359 */
    Lg4 = 2.222219843214978396e-01,                     /* 3FCC71C5 1D8E78AF */
    Lg5 = 1.818357216161805012e-01,                     /* 3FC74664 96CB03DE */
    Lg6 = 1.531383769920937332e-01,                     /* 3FC39A09 D078C69F */
    Lg7 = 1.479819860511658591e-01;                     /* 3FC2F112 DF3E5244 */

static const double zero = 0.0;

double __ieee754_log2(double x) {
  double hfsq, f, s, z, R, w, t1, t2, dk;
  int32_t k, hx, i, j;
  uint32_t lx;

  EXTRACT_WORDS(hx, lx, x);

  k = 0;
  if (hx < 0x00100000) { /* x < 2**-1022  */
    if (((hx & 0x7fffffff) | lx) == 0)
      return -two54 / zero; /* log(+-0)=-inf */
    if (hx < 0)
      return (x - x) / zero; /* log(-#) = NaN */
    k -= 54;
    x *= two54; /* subnormal number, scale up x */
    GET_HIGH_WORD(hx, x);
  }
  if (hx >= 0x7ff00000)
    return x + x;
  k += (hx >> 20) - 1023;
  hx &= 0x000fffff;
  i = (hx + 0x95f64) & 0x100000;
  SET_HIGH_WORD(x, hx | (i ^ 0x3ff00000)); /* normalize x or x/2 */
  k += (i >> 20);
  f = x - 1.0;
  dk = (double)k;
  if ((0x000fffff & (2 + hx)) < 3) { /* |f| < 2**-20 */
    if (f == zero)
      return (dk);
    R = f * f * (0.5 - 0.33333333333333333 * f);
    return (dk - (R - f) / ln2);
  }
  s = f / (2.0 + f);
  z = s * s;
  i = hx - 0x6147a;
  w = z * z;
  j = 0x6b851 - hx;
  t1 = w * (Lg2 + w * (Lg4 + w * Lg6));
  t2 = z * (Lg1 + w * (Lg3 + w * (Lg5 + w * Lg7)));
  i |= j;
  R = t2 + t1;
  if (i > 0) {
    hfsq = 0.5 * f * f;
    return (dk - (hfsq - s * (hfsq + R) - f) / ln2);
  } else
    return (dk - ((s * (f - R)) - f) / ln2);
}
#endif
